The present invention relates to the creation of spatialized sounds utilizing a headtracked set of headphones.
Methods for localizing sounds utilizing headphones and a headtracking unit are known. For example, in U.S. patent Ser. No. 08/723,614 entitled xe2x80x9cMethods and Apparatus for Processing Spatialized Audioxe2x80x9d, there is disclosed a system for virtual localization of a sound field around a listener utilizing a pair of headphones and a headtracking unit which determines the orientation of the headphones relative to an external environment. Unfortunately, the disclosed arrangement requires a high computational power or resource for real time rotation of a sound field environment so as to take into account any headphone movement relative to the desired sound field output.
Alternatively, without headtracking, a virtual speaker system over headphones can be simulated by using a pair of filters for each virtual sound source and then a post mixing of the results to produce left and right signals. For example, turning initially to FIG. 1, if it is desired to simulate to a user 1 over headphones eg. 2, 3 a virtual sound environment, with, for example, the environment comprising the popular Dolby DIGITAL (Trade Mark) environment which includes a left, 5, and right, 6 sound source in addition to a center cell source 7 and back left and right sound sources 8 and 9, then one form of suitable arrangement may be as illustrated 10 in FIG. 2. The arrangement 10 includes, for each channel eg. 11 providing a head related transfer function filter eg. 12, 13 for each input channel which maps the sound source to each of the left and right ears so as to form left and right headphone channels 16, 17. Similarly, each of the other channels is similarly processed and the output summed to each head channel. The arrangement 10 in FIG. 2 is provided for a system that does not utilize headtracking. The arrangement of FIG. 2 requires significant length filters eg. 12, 13 for each channel. Of course, many filter optimisations are possible in respect of the non treadtracked arrangement. An example of these optimisations include those disclosed in PCT Patent Application No. PCT AU99/00002 filed 6 Jan., 1999 by the present applicant entitled xe2x80x9cAudio Signal Processing Method and Apparatusxe2x80x9d.
One possible method utilized by others to perform headtracking is to use an enormous amount of computational memory for storing a large number of sets of filter coefficients. For example, a set of filter coefficients could be stored for every angle around a listener (for full 360 coverage), then, each time the listener rotated their head the filter coefficients could be updated to reflect the new angle. A cross fade to the new filter coefficients would remove any unwanted artefacts. This technique has the significant disadvantage that it requires an enormous amount of memory to store the large number of filtered coefficients.
An alternative technique is disclosed in U.S. Pat. No. 5,659,619 by Abel which utilizes a process of principle component analysis where the head related transfer function is assumed to consist of several individual filter structures which are all modified from a look-up table according to a current head angle. This method provides for a reduction in memory requirements.
However, it is only practical for short filters (short HRTF length) which provide for directionality of a sound source and it is not practical for a full room reverberant response in addition to the effective simulation of a full room.
It would be desirable to provide for a more efficient form of simulation of a sound surround environment over headtracked headphones in addition to the effective simulation of a full room reverberant response.
It is an object of the present invention to provide for a more efficient form of simulation of a surround sound environment over headtracked headphones.
In accordance with a first aspect of the present invention, there is provided a method of simulating a spatial sound environment to a listener over headphones comprising inputting a series of sound signals having spatial components; determining a current orientation of the headphones around the listener; determining a mapping function from a series of spatially static virtual speakers placed around the listener to each ear of the listener; utilising the current orientation to determine a current panning of the sound signals to the series of virtual speakers so as to produce a panned sound input signal for each of the virtual speakers; utilising the mapping function to map the panned sound input signal to each ear of the listener; and combining the mapped panned sound input signals to produce a left and right output signal for the headphones.
Preferably, the virtual speakers include a set of simulated speakers placed at substantially equal angles around the listener which can be placed substantially in a horizontal plane around a listener or placed so as to fully surround a listener in three dimensions. The present invention has particular application wherein the series of sound signals comprise a Dolby DIGITAL encoding of a sound environment.
In accordance with a second aspect of the present invention, there is provided an apparatus for simulating a spatial sound environment to a listener over headphones comprising input means for inputting a series of signals comprising a spatial sound environment; panning means for panning the series of signals amongst a predetermined number of virtual output signals to produce a plurality of virtual output speakers signals; head related transfer function mapping means for mapping the virtual output speaker signals to left and right headphone channel signals; and combining means for combining each of the left and right headphone channel signals into combined left and right headphone signals for playback over the headphones.
Preferably, the panning means, the head related transfer function mapping means and the combining means are implemented in the form of a suitably programmed digital signal processor.